The following patent publications are believed to represent the current state of the art:
U.S. Pat. Nos. 6,351,260; 6,761,457; 4,782,328; 6,690,363 and 6,281,878;
U.S. Patent Application Publication Numbers: 2005/271319 and 2005/190162; and
PCT Patent Publication Numbers: WO04/023208; WO05/043231; WO04/003656 and WO02/054169.